The present invention relates to climbing formwork for use in the erection of reinforced concrete structures and to a method of erecting such structures using climbing formwork.
In the erection of vertically extending reinforced concrete structures, of which the core of a multi-storey reinforced concrete building is a typical example, it is usual to use internal and external forms of a size such that they can be conveniently handled, and to erect the structure section by section moving the formwork upwardly at each section is completed. The core of such buildings is normally a more or less rectangular structure including within it a number of lift shafts, stairwells, ducts and the like. The external formwork is in the form of vertically extending sheets of a material such as plywood, the internal formwork being in the form of hollow boxes which can be collapsed inwardly to assist in stripping the form from the concrete.
One present practice is to raise the formwork section by section by means of a large crane permanently maintained on the site of the building, concrete being cast between the forms to a height corresponding to the height of one storey of the building and after the concrete has set the forms are raised by means of the crane into position to cast the next storey. An alternative procedure which avoids the necessity for the use of a crane is the "slip-form" process in which formwork of limited height is supported by supporting members set in the concrete and is carried by yokes extending from them, the formwork being continually raised as concrete is poured, the rate at which it is raised being such that the concrete will have set off sufficiently to be self supporting once the lower edge of the formwork has been raised above it.
These two systems have certain disadvantages. The maintenance of a large crane on a building site is extremely expensive both in terms of capital invested and of labor costs. While the slip-form method avoids this difficulty its nature is such that it is very difficult to produce a good and uniform finish on the concrete. It also has the disadvantage of requiring the attendance of a technician on the building site the whole time the concrete is being poured to supervise the operation of the sliding formwork.